The present invention relates to an aircraft undercarriage of the type comprising a leg constituted by a strut in which there slides a telescopic rod that forms a shock absorber, the free end of the rod being hinged to a rocker beam carrying a multiple-axle wheel set.
The invention relates more particularly to landing gear in which the leg strut is hinged so as to be capable of being pivoted by an associated connection structure about a substantially horizontal axis that is highly offset from the sliding axis of the telescopic rod which is vertical in the gear-down position.
It has been known for a long time to make landing gear structures in which the pivot axis is not coplanar with the sliding axis of the telescopic rod. Nevertheless, in existing embodiments, the offset is generally relatively small, which has always-made it possible to envisage making a one-piece strut combining both the cylinder portion in which the telescopic rod slides and the lugs that receive the bearings for hinging the landing gear to the aircraft, said bearings defining the pivot axis of the leg, with this being achievable under conditions that are technologically and economically acceptable.
Such structures are illustrated, for example, in document DE-A-29 24741. That document describes a fuselage undercarriage of the type that is raised laterally, in which the strut is hinged to the fuselage about a horizontal axis extending longitudinally and that is offset from the sliding axis of the telescopic rod.
The provision of aircraft of ever-increasing weight has led to landing gear being devised comprising a large number of wheels and/or a plurality of undercarriages fitted with wheel sets. One of the retracting mechanisms envisaged for that kind of landing gear then requires structures in which the pivot axis is highly offset relative to the sliding axis of the telescopic rod, in which case it becomes technologically or economically inconceivable to make the strut as a single piece.
This leads to providing an associated connection structure that provides a mechanical connection between the strut proper and the bearings defining the pivot axis of said strut.
Proposals have already been made to make such a connection structure in integral form or in the form of an assembly of a plurality of bars. Such a configuration is unsuitable for landing gear where the rocker beam carries a large number of wheels because of the inability of the structure to transmit effectively the large twisting moment-that is generated while the aircraft is taxiing, and in particular while it is turning.
A bar structure is thus illustrated in document U.S. Pat. No. 1,914,092, which describes tail landing gear presenting a hinged axis connecting it to the fuselage, which axis is highly offset relative to the pivot axis of the tail wheel. Pivoting of the tail wheel prevents it from transmitting twisting torque to the structure, so a bar configuration is entirely suitable. This would not apply if said structure were to be subjected to twisting.
In a variant, proposals have been made to implement the above-mentioned connection structure in the form of lateral panels each extending in a plane that is vertical when in the gear-down position, the two planes intersecting on the sliding axis of the telescopic rod. That structure is likewise unsuitable for landing gear in which the rocker beam carries a large number of wheels since it is incapable of transmitting high twisting moments effectively as generated when the aircraft is turning while taxiing.
One such structure is illustrated by document GB-A-1 490 088 which relates to landing gear having a complex mechanism in which the strut possesses a hinge axis that is offset relative to the sliding axis of the telescopic rod. To connect the hinge bearings to the cylinder of the strut, the strut is provided with two lateral panels extending in respective planes that are vertical in the gear-down panels with the axis of intersection between the planes coinciding with the sliding axis. To make this structure suitable for withstanding stresses coming from the ground, the lateral panels are provided with thick margins in order to prevent the panels from flexing. That disposition is heavy and ill-adapted to large undercarriages of the type presently under consideration.
The invention seeks to devise a novel landing gear structure that is specially adapted to undercarriages presenting a pivot axis that is substantially horizontal and highly offset relative to the sliding axis of the telescopic rod, which axis is substantially vertical in the gear-down position.
An object of the invention is thus to provide landing gear including a connection structure suitable for transmitting effectively the twisting moments that are generated while the aircraft is taxiing, in particular while it is turning.
In accordance with the invention, this problem is solved by aircraft landing gear of the type comprising a leg constituted by a strut in which a telescopic shock-absorber rod slides along a sliding axis, the free end of the rod being hinged to a rocker beam carrying a wheel set having multiple axles, said strut being hinged to a structure of the aircraft and being capable of being pivoted by an associated connection structure about a substantially horizontal axis that is highly offset from the sliding axis of the telescopic rod which is vertical in the gear-down position. According to the invention, the connection structure is essentially constituted by two panels connecting two axially separate points of the strut to a common axis structure extending along the pivot axis of said strut, in such a manner that in the gear-down position said panels are disposed one above the other, with a top panel which is connected to the strut via a high attachment which is rigid in twisting, and with a bottom-panel which is connected to the strut via a low attachment which tolerates twisting, thereby allowing the strut to warp to some extent when the aircraft is turning while taxiing.
Because of the above-specified attachments, the ability of the low attachment between the bottom panel and the strut to tolerate twisting enables the strut to be warped to some extent when the aircraft is turning while taxiing without that harming the stability of the leg, given that the structure of the high attachment is rigid in twisting.
Preferably, the top panel and the bottom panel both extend in respective planes each containing the pivot axis of the strut, the plane of the top panel being substantially orthogonal to the sliding axis of the telescopic rod.
Advantageously, the top and bottom panels are constituted by plane pieces with stiffened margins.
The high attachment between the top panel and the strut, which attachment is rigid in twisting, may be implemented in various ways, and specific mention may be made of a restrained connection or a connection which is totally rigid by being welded to or being formed integrally with said strut, or indeed a hinged connection about an axis contained in the plane of the panel and extending parallel to the pivot axis of said strut.
The low attachment between the bottom panel and the strut is capable of tolerating twisting and may likewise be made in various ways: for example it may be a connection hinged about an axis contained in the plane of the bottom panel and parallel to the pivot axis of said strut, or a swivel connection associated with a stub axle projecting from the strut, or indeed a restrained connection to at least one lug projecting from said strut.
In general, it is advantageous to provide for the high and low attachments to be level with sliding bearing surfaces for the telescopic rod inside the strut when the rod is in its pushed-in position corresponding to supporting the aircraft on the ground. Thus, while the aircraft is taxiing, loads generated normal to the axis of the strut and passing via said bearing surfaces are countered directly by the top and bottom panels, thus avoiding undesirable bending of the strut.
The common axis structure can be a separate part including the pivot bearings for pivoting the strut about its pivot axis, said separate part being fixed to the top and bottom panels via lugs that are secured to the part and/or to said panels.
In a variant, the common axis structure is integral with one of the panels.
In another variant, the common axis structure includes a panel portion that is fixed to the top panel and/or to the bottom panel, said panel portion being coplanar with and extending the associated panel.